![Bacillus cereus SEM-cr](https://upload.wikimedia.org/wikipedia/commons/5/57/Bacillus_cereus_SEM-cr.jpg)
''Bacillus cereus'' is a
Gram-positive rod-shaped
A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...
bacterium commonly found in
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
, food, and marine sponges.
The specific name, ''cereus'', meaning "waxy" in
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, refers to the appearance of colonies grown on
blood agar
An agar plate is a Petri dish that contains a growth medium solidified with agar, used to Microbiological culture, culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.
Individual microorganism ...
. Some strains are harmful to humans and cause
foodborne illness due to their spore-forming nature, while other strains can be beneficial as
probiotics for animals, and even exhibit mutualism with certain plants.
''B. cereus'' bacteria may be
anaerobes
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenate ...
or
facultative anaerobe
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...
s, and like other members of the genus ''
Bacillus'', can produce protective
endospore
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., no ...
s. They have a wide range of
virulence factors, including
phospholipase C
Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...
,
cereulide
Cereulide is a toxin produced by some strains of ''Bacillus cereus''. It is a potent cytotoxin that destroys mitochondria. It also causes nausea and vomiting.
Cereulide acts as ionophore with a high affinity to potassium cations. Exposure to cere ...
,
sphingomyelinase, metalloproteases, and cytotoxin K, many of which are regulated via
quorum sensing.
''B. cereus'' strains exhibit
flagellar
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have fro ...
motility
Motility is the ability of an organism to move independently, using metabolic energy.
Definitions
Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...
.
The ''Bacillus cereus'' group comprises seven closely related species: ''B. cereus'' ''sensu stricto'' (referred to herein as ''B. cereus''), ''
B. anthracis'', ''
B. thuringiensis'', ''
B. mycoides'', ''
B. pseudomycoides'', and ''
B. cytotoxicus''; or as six species in a ''Bacillus cereus'' sensu lato: ''
B. weihenstephanensis'', ''B. mycoides'', ''B. pseudomycoides'', ''B. cereus'', ''B. thuringiensis'', and ''B. anthracis''.
A phylogenomic analysis combined with average nucleotide identity (ANI) analysis revealed that the ''B. anthracis'' species also includes strains annotated as ''B. cereus'' and ''B. thuringiensis.''
History
Colonies of ''B. cereus'' were originally isolated from a
gelatine plate left exposed to the air in a cow shed in 1887. In the 2010s, examination of
warning letters issued by the
US Food and Drug Administration issued to
pharmaceutical manufacturing
Pharmaceutical manufacturing is the process of industrial-scale synthesis of pharmaceutical drugs as part of the pharmaceutical industry. The process of drug manufacturing can be broken down into a series of unit operations, such as milling, gra ...
facilities addressing facility microbial contamination revealed that the most common contaminant was ''B. cereus''.
Several new enzymes have been discovered in ''B. cereus'', such as
AlkC and
AlkD
AlkD (Alkylpurine glycosylase D) is an enzyme belonging to a family of DNA glycosylases that are involved in DNA repair. It was discovered by a team of Norwegian biologists from Oslo in 2006. It was isolated from a soil-dwelling Gram-positive bact ...
, both of which are involved in
DNA repair
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...
.
Microbiology
![Bacillus cereus endospore stain](https://upload.wikimedia.org/wikipedia/commons/d/d3/Bacillus_cereus_endospore_stain.jpg)
''B. cereus'' is a
rod-shaped
A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...
bacterium with a
Gram-positive cell envelope. Depending on the strain, it may be
anaerobic or
facultatively anaerobic. Most strains are
mesophilic
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organi ...
, having an optimal temperature between 25 °C and 37 °C, and neutralophilic, preferring neutral pH, but some have been found to grow in environments with much more extreme conditions.
These bacteria are both
spore-forming and
biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
-forming, presenting a large challenge to the food industry due to their contamination capability. Biofilms of ''B. cereus'' most commonly form on air-liquid interfaces or on hard surfaces such as glass. ''B. cereus'' display flagellar motility, which has been shown to aid in biofilm formation via an increased ability to reach surfaces suitable for biofilm formation, to spread the biofilm over a larger surface area, and to recruit planktonic, or single, free-living bacteria.
Biofilm formation may also occur while in spore form due to varying adhesion ability of spores.
Their flagella are
peritrichous
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
, meaning there are many flagella located all around the cell body that can bundle together at a single location on the cell to propel it. This flagellar property also allows the cell to change directions of movement depending on where on the cell the flagellum filaments come together to generate movement.
Some studies and observations have shown that silica particles the size of a few nanometers have been deposited in a spore coat layer in the extracytoplasmic region of the ''Bacillus cereus'' spore. The layer was first discovered by the use of scanning transmission electron microscopy (STEM), however the images taken did not have resolution high enough to determine the precise location of the silica. Some investigators hypothesize that the layer helps different spores from sticking together. It has also been shown to provide some resistance to acidic environments. The silica coat is related to the permeability of the cell's inner membrane. Strong mineral acids are able to break down spore permeability barriers and kill the spore. However, when the spore has a silica coating, it may reduce the permeability of the membrane and provide resistance to many acids.
Metabolism
''Bacillus cereus'' has mechanisms for both aerobic and anaerobic respiration, making it a facultative anaerobe.
Its aerobic pathway consists of three terminal oxidases: cytochrome aa3, cytochrome caa3, and cytochrome bd, the use of each dependent on the amount of oxygen present in the environment. The ''B. cereus'' genome encodes genes for metabolic enzymes including NADH dehydrogenases, succinate dehydrogenase, complex III, and cytochrome c oxidase, as well as others. ''Bacillus cereus'' can metabolize several different compounds to create energy, including carbohydrates, proteins, peptides, and amino acids.
The Embden-Meyerhof pathway is the predominant pathway used by ''Bacillus cereus'' to catabolize glucose at every stage of the cell's development, according to estimates of a radiorespirometric method of glucose catabolism. This is true at times of germinative phases, as well as sporogenic phases. At the filamentous, granular, forespore, and transitional stages, the Embden-Meyerhof pathway was responsible for the catabolism of 98% of the cell's glucose. The remainder of the glucose was catabolized by the hexose monophosphate oxidative pathway.
Analysis of the core genome of ''B. cereus'' reveals a limited presence of enzymes meant for breakdown of
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
s and a prevalence of
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...
s and amino acid degradation and transport pathways, indicating that their preferred diet consists of proteins and their breakdown products.
An isolate of a bacterium found to produce
PHBs was identified as ''B. cereus'' through analysis of 16S rRNA sequences as well as similarity of morphological and biochemical characteristics. PHBs may be produced when there is excess carbon or limited essential nutrients present in the environment, and they are later broken down by the microbe as a fuel source under starvation conditions. This indicates the potential role of ''B. cereus'' in producing biodegradable plastic substitutes. PHB production was highest when provided with glucose as a carbon source.
Genomics
The genome of ''B. cereus'' has been characterized and shown to contain over 5 million bp of DNA. Out of these, more than 5500 protein-encoding genes have been identified, of which the top categories of genes with known functions include: metabolic processes, processing of proteins, virulence factors, response to stress, and defense mechanisms. Many of the genes categorized as virulence factors, stress responses, and defense mechanisms encode factors in antibiotic resistance.
There are approximately 600 genes which are common in 99% of the taxa of ''B. cereus'' sensu lato, which constitutes around 1% of all genes in the
pan-genome
In the fields of molecular biology and genetics, a pan-genome (pangenome or supragenome) is the entire set of genes from all strains within a clade. More generally, it is the union of all the genomes of a clade. The pan-genome can be broken d ...
. Due to the prevalence of horizontal gene transfer among bacteria, the pan-genome of ''B. cereus'' is continually expanding. The GC content of its DNA across all strains is approximately 35%.
Following exposure to non-lethal acid shock at pH 5.4-5.5, the
arginine deiminase
In enzymology, an arginine deiminase () is an enzyme that catalyzes the chemical reaction
:L-arginine + H2O \rightleftharpoons L-citrulline + NH3
Thus, the two substrates of this enzyme are L-arginine and H2O, whereas its two products are L ...
gene in ''B. cereus'', ''arcA,'' shows substantial up-regulation. This gene is part of the ''arcABC'' operon which is induced by low-pH environments in ''Listeria monocytogenes'', and is associated with growth and survival in acidic environments. This suggests that this gene is also important for survival of ''B. cereus'' in acidic environments.
The activation of virulence factors has been shown to be transcriptionally regulated via
quorum-sensing
In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...
in ''B. cereus.'' The activation of many virulence factors secreted is dependent on the activity of the Phospholipase C regulator (PlcR), a transcriptional regulator which is most active at the beginning of the
stationary phase of growth. A small peptide called PapR acts as the effector in the quorum-sensing pathway, and when reimported into the cell, it interacts with PlcR to activate transcription of these virulence genes.
When point mutations were introduced into the plcR gene using the CRISPR/Cas9 system, it was observed that the mutated bacteria lost their hemolytic and phospholipase activity.
The flagella of ''B. cereus'' are encoded by 2 to 5 ''fla'' genes, depending on the strain.
Identification
For the isolation and enumeration of ''B. cereus'', there are two standardized methods by
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
(ISO): ISO 7932 and ISO 21871. Because of ''B. cereus'' ability to produce
lecithinase Lecithinase is a type of phospholipase that acts upon lecithin.
It can be produced by ''Clostridium perfringens'', ''Staphylococcus aureus'', ''Pseudomonas aeruginosa'' or ''Listeria monocytogenes''. ''C. perfringens'' alpha toxin (lecithinase) c ...
and its inability to ferment
mannitol, there are some proper
selective media for its isolation and identification such as mannitol-egg yolk-polymyxin (MYP) and polymyxin-pyruvate-egg yolk-mannitol-bromothymol blue agar (PEMBA). ''B. cereus'' colonies on MYP have a violet-red background and are surrounded by a zone of egg-yolk precipitate.
Below is a list of differential techniques and results that can help to identify ''B. cereus'' from other bacteria and ''Bacillus'' species.
*
Anaerobic growth: Positive
*
Voges Proskauer test Voges is a surname. Notable people with the surname include:
*Adam Voges (born 1979), Australian cricketer and coach
* Carol Voges (1925–2001), Dutch illustrator and cartoonist
*Danie Voges (born 1954), South African professional wrestler
* Gerri ...
: Positive
* Acid produced from
** -glucose: Positive
** -arabinose: Negative
** -xylose: Negative
** -mannitol: Negative
* Starch
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
: Positive
*
Nitrate reduction
An algae scrubber is a water filtering device (not to be confused with a scrubber pad used to clean glass) which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow saltwater, fres ...
: Positive
* Degradation of
tyrosine
-Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...
: Positive
* Growth at
** above 50 °C: Negative
* Use of
citrate: Positive
The Central Public Health Laboratory in the United Kingdom tests for motility, hemolysis, rhizoid growth, susceptibility to γ-phage, and fermentation of ammonium salt-based glucose but no mannitol, arabinose, or xylose.
Growth
The optimal growth temperature range for ''B. cereus'' is 30-40 °C.
At , a population of ''B. cereus'' can double in as little as 20 minutes or as long as 3 hours, depending on the food product.
Ecology
Like most ''
Bacilli,'' the most common ecosystem of ''Bacillus cereus'' is the soil. In concert with
Arbuscular mycorrhiza (and
Rhizobium leguminosarum
''Rhizobium leguminosarum'' is a bacterium which lives in a mutualistic symbiotic relationship with legumes, and has the ability to fix free nitrogen from the air. ''R. leguminosarum'' has been very thoroughly studied—it has been the subject ...
in
clover
Clover or trefoil are common names for plants of the genus ''Trifolium'' (from Latin ''tres'' 'three' + ''folium'' 'leaf'), consisting of about 300 species of flowering plants in the legume or pea family Fabaceae originating in Europe. The genus ...
), they can up-regulate plant growth in
heavy metal soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
s by decreasing heavy metal concentrations via bioaccumulation and biotransformation in addition to increasing phosphorus, nitrogen, and potassium uptake in certain plants.
''B. cereus'' was also shown to aid in survival of earthworms in heavy metal soils resulting from the use of metal-based fungicides, showing increases in biomass, reproduction and reproductive viability, and a decrease in metal content of tissues in those inoculated with the bacterium.
These results suggest strong possibilities for its application in ecological
bioremediation. Evidence of bioremediation potential by ''Bacillus cereus'' was also found in the aquatic ecosystem, where organic nitrogen and phosphorus wastes polluting a eutrophic lake were broken down in the presence of ''B. cereus''.
In a study measuring the ability of ''B. cereus'' to degrade keratin in chicken feathers, bacteria were found to sufficiently biodegrade keratin via hydrolytic mechanisms. These results indicate its potential to degrade keratinous waste from the poultry industry for potential recycling of the byproducts.
''B. cereus'' competes with Gram-negative bacteria species such as ''
Salmonella
''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
'' and ''
Campylobacter
''Campylobacter'' (meaning "curved bacteria") is a genus of Gram-negative bacteria. ''Campylobacter'' typically appear comma- or s-shaped, and are motile. Some ''Campylobacter'' species can infect humans, sometimes causing campylobacteriosis, a d ...
'' in the
gut; its presence reduces the number of Gram-negative bacteria, specifically via antibiotic activity via enzymes such as
cereins that impede their quorum sensing ability and exhibit
bactericidal
A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics.
However, material surfaces can also have bactericidal properties based solely on their ...
activity.
In food animals such as
chickens
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...
,
rabbit
Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit speci ...
s and
pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
s, some harmless strains of ''B. cereus'' are used as a probiotic
feed additive A feed additive is an additive of extra nutrient or drug for livestock. Such additives include vitamins, amino acids, fatty acids, minerals, pharmaceutical, fungal products and steroidal compounds. The additives might impact feed presentation, hygi ...
to reduce ''Salmonella'' in the animals'
intestine
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...
s and
cecum. This improves the animals' growth, as well as food safety for humans who eat them. In addition, B. cereus create and release enzymes that aid in the digestion of materials that are typically difficult to digest, such as woody plant matter, in the guts of other organisms.
The strain is a
biofungicide.
[
] A study by Figueroa-López ''et al.'' showed that the presence of this strain reduced ''
Fusarium verticillioides
''Fusarium verticillioides'' is the most commonly reported fungal species infecting maize (''Zea mays''). ''Fusarium verticillioides'' is the accepted name of the species, which was also known as ''Fusarium moniliforme''. The species has also bee ...
'' growth.
B25 shows promise for reduction of
mycotoxin concentrations in
grain
A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...
s.
Pathogenesis
''B. cereus'' is responsible for a minority of foodborne illnesses (2–5%), causing severe
nausea
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
,
vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
, and
diarrhea
Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
. ''Bacillus'' foodborne illnesses occur due to survival of the bacterial endospores when infected food is not, or is inadequately, cooked. Cooking temperatures less than or equal to allow some ''B. cereus''
spores to survive.
This problem is compounded when food is then improperly
refrigerated
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
, allowing the endospores to germinate. Cooked foods not meant for either immediate consumption or rapid cooling and refrigeration should be kept at temperatures below or above .
Germination and growth generally occur between 10 °C and 50 °C,
though some strains can
grow at low temperatures, and Bacillus cytotoxicus strains have been shown to grow at temperatures up to . Bacterial growth results in production of
enterotoxin
An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines.
Enterotoxins are chromosomally encoded or plasmid encoded exotoxins that are produced and secreted from several bacterial organisms. They are heat labi ...
s, one of which is highly resistant to heat and acids (
pH levels between 2 and 11);
ingestion leads to two types of illness: diarrheal and emetic (vomiting) syndrome.
The enterotoxins produced by ''B. cereus'' have beta-hemolytic activity.
* The diarrheal type is associated with a wide range of foods, has an 8-to-16-hour
incubation time
Incubation period (also known as the latent period or latency period) is the time elapsed between exposure to a pathogenic organism, a chemical, or ionizing radiation, radiation, and when symptoms and signs are first apparent. In a typical infect ...
, and is associated with diarrhea and gastrointestinal pain. Also known as the 'long-incubation' form of ''B. cereus'' food poisoning, it might be difficult to differentiate from poisoning caused by ''
Clostridium perfringens''.
Enterotoxin can be inactivated after heating at for 5 minutes, but whether its presence in food causes the symptom is unclear, since it degrades in stomach enzymes; its subsequent production by surviving ''B. cereus'' spores within the
small intestine
The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...
may be the cause of illness.
* The 'emetic' form commonly results from rice which is cooked at a time and temperature insufficient to kill any spores present, then improperly refrigerated. The remaining spores can produce a
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849– ...
,
cereulide
Cereulide is a toxin produced by some strains of ''Bacillus cereus''. It is a potent cytotoxin that destroys mitochondria. It also causes nausea and vomiting.
Cereulide acts as ionophore with a high affinity to potassium cations. Exposure to cere ...
, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption. Distinguishing from other short-term bacterial foodborne intoxications, such as by ''
Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...
,'' can be difficult.
Emetic toxin can withstand for 90 minutes.
The diarrhetic syndromes observed in patients are thought to stem from the three toxins:
hemolysin
Hemolysins or haemolysins are lipids and proteins that cause lysis of red blood cells by disrupting the cell membrane. Although the lytic activity of some microbe-derived hemolysins on red blood cells may be of great importance for nutrient acqu ...
BL (Hbl), nonhemolytic
enterotoxin
An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines.
Enterotoxins are chromosomally encoded or plasmid encoded exotoxins that are produced and secreted from several bacterial organisms. They are heat labi ...
(Nhe), and
cytotoxin K (CytK). The ''nhe''/''hbl''/''cytK'' genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by ''PlcR''. These genes occur in the taxonomically related
''B. thuringiensis'' and
''B. anthracis'', as well. These enterotoxins are all produced in the small intestine of the host, thus thwarting digestion by host endogenous enzymes. The Hbl and Nhe toxins are pore-forming toxins closely related to
ClyA of ''
E. coli''. The proteins exhibit a conformation known as a "
beta-barrel" that can insert into cellular membranes due to a
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
exterior, thus creating pores with
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
interiors. The effect is loss of cellular
membrane potential
Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...
and eventually cell death.
Previously, it was thought that the timing of the toxin production was responsible for the two different courses of disease, but it has since been found that the emetic syndrome is caused by the toxin
cereulide
Cereulide is a toxin produced by some strains of ''Bacillus cereus''. It is a potent cytotoxin that destroys mitochondria. It also causes nausea and vomiting.
Cereulide acts as ionophore with a high affinity to potassium cations. Exposure to cere ...
, which is found only in emetic strains and is not part of the "standard toolbox" of ''B. cereus''. Cereulide is a cyclic polypeptide containing three repeats of four amino acids: -oxy-—-—-oxy-—- (similar to
valinomycin
Valinomycin is a naturally occurring dodecadepsipeptide used in the transport of potassium and as an antibiotic. Valinomycin is obtained from the cells of several '' Streptomyces'' species, '' S. fulvissimus'' being a notable one.
It is a member ...
produced by ''
Streptomyces griseus'') produced by
nonribosomal peptide synthesis. Cereulide is believed to bind to 5-hydroxytryptamine 3 (5-HT3)
serotonin
Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...
receptors, activating them and leading to increased
afferent
Afferent may refer to:
Anatomical structures
Meaning "conveying towards a center":
* Afferent arterioles, blood vessels that supply the nephrons
* Afferent lymphatic vessels, lymph vessels that carry lymph to a lymph node
* Afferent nerve fiber ...
vagus nerve stimulation. It was shown independently by two research groups to be encoded on multiple
plasmid
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...
s: pCERE01 or pBCE4810. Plasmid pBCE4810 shares homology with the ''B. anthracis'' virulence plasmid pXO1, which encodes the
anthrax toxin
Anthrax toxin is a three-protein exotoxin secreted by virulent strains of the bacterium, ''Bacillus anthracis''—the causative agent of anthrax. The toxin was first discovered by Harry Smith in 1954. Anthrax toxin is composed of a cell-binding ...
. Periodontal isolates of ''B. cereus'' also possess distinct pXO1-like plasmids. Like most of cyclic peptides containing nonproteogenic amino acids, cereulide is resistant to heat, proteolysis, and acid conditions.
''B. cereus'' is also known to cause difficult-to-eradicate chronic skin infections, though less aggressive than
necrotizing fasciitis. ''B. cereus'' can also cause
keratitis
Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired e ...
.
While often associated with gastrointestinal illness, ''B. cereus'' is also associated with illnesses such as fulminant bacterial infection, central nervous system involvement, respiratory tract infection, and endophthalmitis. Endophthalmitis is the most common form of extra-gastrointestinal pathogenesis, which is an infection of the eye that may cause permanent vision loss. Infections typically cause a corneal ring abscess, followed by other symptoms such as pain, proptosis, and retinal hemorrhage. While different from ''B. anthracis, B. cereus'' contains some toxin genes originally found in ''B. anthracis'' that are attributed to anthrax-like respiratory tract infections.
A case study was published in 2019 of a
catheter-related bloodstream infection of ''B. cereus'' in a 91-year-old male previously being treated with
hemodialysis via PermCath for end-stage
renal disease
Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease of a kidney. Nephritis is an inflammatory kidney disease and has several types according to the location of the inflammation. Inflammation can b ...
. He presented with chills,
tachypnea
Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing.
In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea be ...
, and high-grade fever, his
white blood cell count
A complete blood count (CBC), also known as a full blood count (FBC), is a set of medical laboratory tests that provide information about the cells in a person's blood. The CBC indicates the counts of white blood cells, red blood cells and pl ...
and
high-sensitivity C-reactive protein
C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin- ...
(CRP) were significantly elevated, and
CT imaging
A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...
revealed a thoracic
aortic aneurysm
An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. They usually cause no symptoms except when ruptured. Occasionally, there may be abdominal, back, or leg pain. The prevalence of abdominal aortic ...
. He was successfully treated for the aneurysm with intravenous
vancomycin
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, ...
, oral
fluoroquinolones, and PermCath removal. Another case study of ''B. cereus'' infection was published in 2021 of a 30 year old woman with lupus who was diagnosed with infective endocarditis after receiving a catheter. The blood samples were positive for B. cereus and the patient was subsequently treated with vancomycin. PCR was also used to verify toxins that the isolate produces.
Diagnosis
In case of
foodborne illness, the diagnosis of ''B. cereus'' can be confirmed by the isolation of more than 100,000 ''B. cereus'' organisms per gram from epidemiologically-implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting.
Prognosis
Most emetic patients recover within 6 to 24 hours,
but in some cases, the toxin can be fatal via
fulminant hepatic failure
Acute liver failure is the appearance of severe complications rapidly after the first signs (such as jaundice) of liver disease, and indicates that the liver has sustained severe damage (loss of function of 80–90% of liver cells). The complicat ...
. In 2014, 23 newborns in the UK receiving
total parenteral nutrition contaminated with ''B. cereus'' developed
sepsis
Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...
, with three of the infants later dying as a result of infection.
Prevention
While ''B. cereus'' vegetative cells are killed during normal cooking, spores are more resistant. Viable spores in food can become vegetative cells in the intestines and produce a range of diarrheal enterotoxins, so elimination of spores is desirable. In wet heat (poaching, simmering, boiling, braising, stewing, pot roasting, steaming), spores require more than 5 minutes at at the coldest spot to be destroyed. In dry heat (grilling, broiling, baking, roasting, searing, sautéing), for 1 hour kills all spores on the exposed surface.
This process of eliminating spores is very important, as spores of ''B. cereus'' are particularly resistant, even after pasteurization or exposure to gamma rays.
''B. cereus'' and other members of ''Bacillus'' are not easily killed by alcohol; they have been known to colonize distilled liquors and alcohol-soaked swabs and pads in numbers sufficient to cause infection.
A study of an isolate of ''Bacillus cereus'' that was isolated from the stomach of a sheep was shown to be able to break down β-cypermethrin, or β-CY, which has been known to be an antimicrobial agent. This strain, known as GW-01, can break down β-CY at a significant rate when the bacterial cells are in high concentrations relative to the antimicrobial agent. It has also been noted that the ability to break down β-CY is inducible. However, as the concentration of β-CY increases, the rate of β-CY degradation decreases. This suggests that the agent also functions as a toxin against the GW-01 strain. This is significant as it shows that in the right concentrations, β-CY can be used as an antimicrobial agent against ''Bacillus cereus''.
Diseases in aquatic animals
''Bacillus cereus'' groups, notably ''B. cereus (Bc)'' and ''B. thuringiensis (Bt),'' are also pathogenic to multiple aquatic organisms including Chinese softshell turtle ( ''Pelodiscus sinensis'' ), causing infection characterized by gross lesions such as hepatic congestion and enlarged spleen, which causes high mortality.
Bacteriophages
Bacteria of the ''B. cereus'' group are infected by
bacteriophage
A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...
s belonging to the family
Tectiviridae. This family includes tailless phages that have a
lipid membrane or vesicle beneath the icosahedral protein shell and that are formed of approximately equal amounts of virus-encoded proteins and
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
s derived from the host cell's
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
. Upon infection, the lipid membrane becomes a tail-like structure used in genome delivery. The genome is composed of about 15-
kilobase, linear, double-stranded
DNA (dsDNA) with long, inverted terminal-repeat sequences (100 base pairs). GIL01, Bam35, GIL16, AP50, and Wip1 are examples of temperate tectiviruses infecting the ''B. cereus'' group.
See also
*
''Bacillus cereus'' biovar ''anthracis''
References
External links
Bacillus cereusgenomes and related information a
PATRIC a Bioinformatics Resource Center funded b
NIAIDType strain of ''Bacillus cereus'' at Bac''Dive'' – the Bacterial Diversity Metadatabase
{{Authority control
cereus
Foodborne illnesses
Bacteria described in 1887